Method and apparatus for transmitting position information on a digital map

ABSTRACT

The invention purposes to provide a position information transmission method for accurately transmitting a position and a shape on a digital map with a small amount of data.  
     In a position information transmission method of the invention, the transmitting side transmits road shape information to specify the target road section on a digital map and event information to specify an event position by using a relative position in the target road section and the receiving side performs map matching based on the road shape information to identify the target road section and identifies the event position in the target road section based on the event information is characterized in that the transmitting side intermittently selects nodes included in the target road section to include the coordinate data of the nodes in the road shape information for transmission, and that the receiving side performs map matching to determine the positions of the nodes included in the road shape information and obtains the road connecting the nodes by way of a route search to identify the target road section. It is thus possible to efficiently and accurately transmit an event position on a digital map.

TECHNICAL FIELD

[0001] The present invention relates to a method for transmittingposition information on a digital map and apparatus for implementing themethod, and in particular to a method and apparatus for accuratelytransmitting position information on a digital map by using only a smallamount of data.

BACKGROUND OF THE INVENTION

[0002] In recent years, the number of vehicles that have on-boardnavigation apparatus has been increasing rapidly. The on-boardnavigation apparatus maintains a digital map database and is capable ofdisplaying traffic congestion and traffic accident positions on the mapbased on traffic congestion information and traffic accident informationprovided by a traffic information center as well as performing a routesearch using conditions including the aforementioned information.

[0003] In Japan, digital map databases are prepared by severalcompanies. The problem is that map data contains errors due to thedifferent base maps and digitizing technologies. The error depends onthe digital map from each publisher.

[0004] In the traffic information, for example, in caselatitude/longitude data of the position is presented alone in order toreport for example a traffic accident position, on-board navigationapparatus may identify a different point on the road as a trafficaccident position depending on the type of the digital databasemaintained by the apparatus.

[0005] In order to offset such incorrect transmission of information, inthe related art, node numbers are defined for nodes such asintersections in a road network and link numbers are defined for linksrepresenting roads connecting nodes. A digital map database from eachpublisher stores intersections and roads in correspondence to nodenumbers and link numbers. For traffic information, a road number isidentified by a link number and a point on the road is displayed in arepresentation that the road is XX meters away from the start of thelink.

[0006] However, node numbers and link numbers defined on a road networkmust be changed to new numbers in case a road is constructed ormodified. When a node number or link number is changed, the digital mapdatabase from each publisher must be updated. Thus, the method fortransmitting position information on a digital map requires a huge costof maintenance.

[0007] In order to solve such problems, the inventor of the inventionproposed, in the Japanese Patent Application No. 214068/1999, a systemwhere an information providing side transmits “road shape data”including a coordinate string showing the road shape in the road sectionof a predetermined length including the on-road position and “relativeposition data” showing the on-road position in the road sectionrepresented by the road shape data in order to report the on-roadposition, and a receiving side uses the road shape data to perform mapmatching, identifies the road section on a digital map, and uses therelative position data to identify the on-road position in the roadsection. The inventor proposed, in the Japanese Patent Application No.242166/1999, a system where “supplementary information” is alsotransmitted including the road type, road number, number of crossinglinks in the road section, crossing link angles and intersection names,and a system where the transmission data amount of “road shape data” isreduced without causing erroneous matching at the receiving side.

[0008] In this case, map matching at the receiving side is made forexample as follows:

[0009] As shown in FIG. 21, when the longitude/latitude data of thepoint P₀ (x₀, y₀), P₁(x₁, y₁), . . . , p_(k)(X_(k),y_(k)) is transmittedas (x₀, y₀) (x₁, y₁), . . . , (x_(k), y_(k)), the receiving side usesthe map data read from its digital map database to select roads includedin the error range about the point P₀ (x₀, y₀) as candidates, andnarrows down the candidates by using the transmitted “supplementaryinformation.” When a single candidate is finally selected, a positionclosest to the point P₀ (x₀, y₀) and the point P_(k) (x_(k), y_(k)) onthe road is obtained, and the section is assumed as a road sectionrepresented by the “road shape data.”

[0010] When the final candidate is not selected but the roads Q, R areselected as candidates, the points Q₀, R₀ on the candidate roads closestto the point P₀ (x₀, y₀) are obtained to calculate distance between P₀and Q₀ and the distance between P₀ and R₀. This operation is repeatedfor each point P₁ (x₁, y₁), . . . , P_(k) (x_(k), y_(k)) and a roadsection where the sum of the root mean square of the distances from eachpoint P₀, P₁, . . . , p_(k) is smallest is obtained. This section isassumed as a road section represented by “road shape data” to identifythe road section.

[0011] The traffic congestion section A-B is identified based on“relative data” transmitted from the start point of the road sectionobtained from “road shape data.”

DISCLOSURE OF THE INVENTION

[0012] In the system where road shape data is transmitted, however, howto reduce the transmission data amount without degrading the informationaccuracy is a major problem. The inventor, in order to reduce the dataamount, proposed a system whereby the shape data of the linear roadsections is reduced and a system where the curve shape of a road isrepresented by Fourier coefficients, approximated by arcs, orrepresented by spline function to compress the data amount. In case, asshown in FIG. 23, the road density is low but the road shape iscomplicated and an interval between nodes is longer, as on the roads inthe mountains, using such a system still requires a large amount of datato represent the road shape.

[0013] The invention solves such related art problems and aims atproviding a position information transmission method for accuratelytransmitting a position and a shape on a digital map using a smallamount of data and apparatus for implementing the method.

[0014] According to the invention, a position information transmissionmethod wherein the transmitting side transmits road shape information tospecify the target road section on a digital map and event informationto specify an event position by using a relative position in the targetroad section and the receiving side performs map matching based on theroad shape information to identify the target road section andidentifies the event position in the target road section based on theevent information is characterized in that the transmitting sideintermittently selects nodes included in the target road section toinclude the coordinate data of the nodes in the road shape informationfor transmission, and that the receiving side performs map matching todetermine the positions of the nodes included in the road shapeinformation and obtains the road connecting the nodes by way of a routesearch to identify the target road section.

[0015] The transmitting side evaluates the potential for erroneousmatching of the nodes in the target road section at the receiving side,and determines the length of the target road section or the number ofnodes to be included in the road shape information.

[0016] The present invention also provide a position informationtransmission apparatus for transmitting road shape information tospecify the target road section on a digital map and event informationto specify an event position by using a relative position in the targetroad section. The transmission apparatus is characterized in that theapparatus includes position information converting means for selecting atarget road section having the event position and transmit nodeextracting means for intermittently selecting nodes to be included inthe road shape information out of the nodes arranged on the target roadsection.

[0017] The present invention further provide a position informationreceiving apparatus for receiving road shape information to specify thetarget road section on a digital map and event information to specify anevent position by using a relative position in the target road sectionis characterized in that the apparatus comprises map matching means forperforming map matching to determine the positions of the nodes includedin the road shape information and route search means for obtaining theroad connecting the nodes determined to reproduce the target roadsection.

[0018] This makes it possible to transmit event positions on a digitalmap efficiently and accurately with a small data amount thus enhancingthe data transmission efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a schematic view of a position information transmissionmethod according to the first embodiment. FIG. 1 (1) shows theprocessing at the transmission apparatus and FIG. 1 (2), (3) and (5)shows processing at the receiving apparatus. FIG. 1 (1) is a schematicview of a process of selecting target roads, (2) selecting nodes to betransmitted, (3) plotting received nodes on the map of the receivingapparatus, (4) calculating the road position on the local map, and (5)connecting the calculated nodes with the shortest route search todetermine the target road or section.

[0020]FIG. 2 is a block diagram showing the configuration of positioninformation receiving apparatus according to the first embodiment of theinvention.

[0021]FIG. 3 is a flowchart showing a position information transmissionmethod according to the first embodiment,

[0022] FIGS. 4(a), (b), (c), (d) and (e) show and example of dataconfiguration in the position information transmission method accordingto the first embodiment. FIG. 4(a) represents shape vector data stringinformation for identifying roads and sections. FIG. 4(b) shows variousroad information represented by a relative distance from each node afterthe road section is identified. FIG. 4(c) shows an absolutelatitude/longitude representation, (c) a lot normalization coordinaterepresentation, and (e) a curvature function representation. FIG. 4(f)explains the deflection angle in the curvature function representation.

[0023] FIGS. 5(a) and (b) show other data configuration examples of aposition information transmission method according to the firstembodiment. FIG. 5(a) shows shape vector data string information withroad type or number for identifying roads and sections. FIG. 5(b) showssupplementary information to facilitate identification of nodes.

[0024]FIG. 6 explains a connection link angle.

[0025]FIG. 7 shows a route search referring to supplementary informationby way of a position information transmission method according to thefirst embodiment.

[0026]FIG. 8 shows an intercept azimuth to be transmitted from thetransmitting side by way of a position information transmission methodaccording to the second embodiment.

[0027]FIG. 9 explains map matching at the receiving side in a positioninformation transmission method according to the second embodiment.

[0028]FIG. 10 explains how to obtain the intercept azimuth.

[0029]FIG. 11 shows a processing flow at the transmitting side in aposition information transmission method according to the secondembodiment.

[0030]FIG. 12 shows a map matching flow at the receiving side in aposition information transmission method according to the secondembodiment.

[0031]FIG. 13 shows a data configuration example of a positioninformation transmission method according to the second embodiment andillustrates vector data string information for identifying roads andsections.

[0032] FIGS. 14(1), (2), (3), (4), and (5) are schematic views of aposition information transmission method according to the thirdembodiment. FIGS. 14(1) and (2) show processing at the transmissionapparatus and (3), (4) and (5) processing on receiving apparatus. FIG.14(1) is a schematic view of a process of selecting target roads, (2)selecting nodes to be transmitted, (3) plotting received nodes on themap of the receiving apparatus, (4) calculating the road position on thelocal map, and (5) connecting the calculated nodes with the shortestroute search to determine the target road or section.

[0033]FIG. 15 shows a data configuration example of a positioninformation transmission method according to the third embodiment andillustrates vector data string information for identifying roads andsections.

[0034]FIG. 16 explains the distance to an adjacent road and differencein the intercept azimuth angle used for decision in the positioninformation transmission method according to the third embodiment.

[0035]FIG. 17 shows a processing flow in a position informationtransmission method according to the third embodiment.

[0036]FIG. 18 shows a processing flow at the transmission apparatus in aposition information transmission method according to the fourthembodiment.

[0037]FIG. 19 shows a processing flow at the receiving apparatus in aposition information transmission method according to the fourthembodiment.

[0038]FIG. 20 shows a data configuration example of a positioninformation transmission method according to the fourth embodiment andillustrates vector data string information for identifying roads andsections.

[0039]FIG. 21 explains an example of map matching.

[0040]FIG. 22 explains road shape data and relative positioninformation.

[0041]FIG. 23 is a printout photo of a map showing the road shape in themountains.

[0042] In the figures, numerals 10, 20 represent position informationtransmission/receiving apparatus, 11, 22 a position informationreceiver, 12 a map matching section, 13 a route search section, 14 adigital map database, 15 a digital map display section, 16 an eventinformation input section, 17 a position information converter, 18 atransmit node group/supplementary information extracting section, and19, 21 a position information transmitter.

BEST MODE FOR CARRYING OUT THE INVENTION

[0043] (First Embodiment)

[0044] According to a position information transmission method of theinvention, a transmitting side selects a small number of nodes (whichmay be two points, start point and end point) out of the nodes includedin a road section to be transmitted, and transmits the node information.A receiving side performs a map matching to determine the positions ofthe received nodes and sequentially searches for the shortest routesconnecting the nodes, then links the shortest routes to identify theroad section.

[0045]FIG. 2 shows the configuration of the position informationtransmission/receiving apparatus 10 that exchanges event informationoccurring in the jurisdiction with other apparatus 20.

[0046] The apparatus 10 includes a position information receiver 11 forreceiving position information sent from the position informationtransmitter 21 of the other apparatus 20, a digital map database 14 foraccumulating digital map data, a map matching section 12 for identifyingthe corresponding node position from the node information included inthe received information by using a map matching, a route search sectionfor searching for the shortest routes connecting nodes, a digital mapdisplay section 15 for displaying the event position on a map, an eventinformation input section 16 for inputting event information, a positioninformation converter 17 for displaying the event position by using therelative position of the target road section represented by road shapedata, a transmit node group/supplementary information extracting section18 for selecting nodes in the target road section whose node informationis to be transmitted and supplementary information to be transmitted,and a position information transmitter 19 for sending the positioninformation on the selected nodes together with the selectedsupplementary information to the position information receiver 22 of theother apparatus 20.

[0047] The digital map database 14 includes node data and link data on adigital map. The node data includes the latitude/longitude coordinatedata of nodes, data of node type (identification information such asintersections, entrance and exit of a tunnel, interchange tollgates,road attribute change points, boundaries of prefectures, boundaries ofsecondary mesh, and landmarks), names, number of connection links toconnect to nodes, and connection link angle representing the angle ofthe connection link. The link data includes data such as the roadnumber, the road type (identification information on national highway,prefectural roads, and municipal roads), the link type (identificationinformation on the main line, interchange entrance/exit, links in anintersection, byroads, connection roads and interlinking roads),presence/absence of traffic prohibition and direction of trafficprohibition, various costs of each link represented by distance ortravel time, as well as interpolation point coordinate data representinga link shape. The interpolation points are points set to represent aninter-node road shape. Here, unless otherwise specified, nodes andinterpolation points where coordinate data is maintained are callednodes. Node data and link data on a digital map includes rivers,administrative boundaries, contour lines and houses. Node data and linkdata other than node data of roads has inherent type and attribute codealthough the configuration is the same as that on roads. Thus the systemcan be applied to node data and link data other than road data. Thecoordinate data includes data represented by latitude and longitude,relative latitude/longitude representation with respect to thepreceding/subsequent node, normalized coordinate representation in apredetermined section number and curvature function representation(relative polar coordinate representation with respect to thepreceding/subsequent node).

[0048]FIG. 3 individually shows the processing procedure on thetransmitting side and receiving side. FIGS. 1(1), (2), (3), (4), and (5)are schematic views of the individual processing details on a map.

[0049] Step 1: When the information to report an event such as a trafficcongestion and traffic accident is input from the event informationinput section 16, the position information converter 17 selects a roadsection including the event position as a target road section based onthe data in the digital map database 14 and generates trafficinformation displaying the event position by using the relative distancefrom the reference point of the target road section. FIG. 1(1) shows theselected target road section. Solid filled circles on the targetembodiment show the nodes whose coordinate data is maintained in thedigital map database 14.

[0050] Step 2: The transmit node group/supplementary informationextracting section 18 selects nodes whose node information is to betransmitted out of the nodes in the target road section. As shown inFIG. 1(2), the nodes at the start point (p₁) and the end point (p₃) ofthe target road section must be selected. The nodes selected may bethese two, but may include those selected intermittently, that is, inintervals of several hundreds of meters to several kilometers. In thisexample, an intermediate node p₂ is additionally selected.

[0051] Step 3: Information that enhances the accuracy of map matchingand a route search is extracted as required as supplementary informationout of the node data of the selected nodes and link data of the targetroad section.

[0052] Step 4: The position information transmitter sends shape vectordata string information comprising coordinate data of the selected nodesand selected supplementary information to represent the target roadsection and traffic information to represent the event position by therelative distance from the reference point of the target road section.

[0053] FIGS. 4(a), (b), (c) and (d) shows shape vector data stringinformation without supplementary information. FIG. 4 (b) shows trafficinformation including event position information represented by therelative distance from the reference point of the target road sectionand event detail information. The shape vector data string informationmay be represented by various coordinate data as mentioned earlier, butmay be any data as long as it attains the present application. In thecurvature function representation in FIG. 4(e), a deflection angle shownin FIG. 4(f) is used. The following description uses the example of FIG.4 (a). In the relative coordinate representation in FIG. 4(a), thecoordinates of the start node is represented by absolute coordinates(longitude/latitude) and the coordinates of the remaining nodes byrelative coordinates with respect to the start node (or preceding nodein the line of nodes) in order to reduce the data amount. A referencepoint of the target road section in the traffic information may be thenode p₂ halfway in the target road section instead of the start point(p₁) and end point (p₃) .

[0054]FIG. 5(a) shows shape vector data string information assupplementary information including the link data such as the road type,road number and link type. FIG. 5(b) shows shape vector data stringinformation as supplementary information including the node data such asthe node type, node name, number of connecting links of the node, andangle between connecting links. The angle between connecting links isdisplayed by the angle θ1 to θ4 with respect to the absolute azimuth ofthe true north (dotted line) at the node (node type=intersection, name=4cho-me, Tsunashima)

[0055] At the receiving side,

[0056] Step 5: The position information receiver 11 receives the shapevector data string information and the traffic information.

[0057] Step 6: The map matching section 12 uses the data in the digitalmap database 14 to perform map matching and determines the position ofthe nodes included in the shape vector data string information. In casethe shape vector data string information includes supplementaryinformation, the map matching section 12 uses the supplementaryinformation to execute map matching.

[0058]FIG. 1 (3) shows the plotting result of the received nodes p₁, p₂and p₃ on the map of the receiving side. In case the publisher of thedigital map data owned by the transmitting side differs from thepublisher of the digital map data owned by the receiving side, such a“disposition” occurs frequently.

[0059]FIG. 1(4) shows a state where the position of the nodes p₁′, p₂′and p₃′ corresponding to the nodes p₁, p₂ and p₃ on the map of thereceiving side are determined. Even in case a nearby intersection existsthat may be cause erroneous matching with p₁ around the node p₁ as shownin FIG. 7, matching with a correct node position is made possible byreferencing supplementary information such as node name.

[0060] Step 7: The route search section 13 uses the link costrepresented by the distance of the link data in the digital map database14 to sequentially searches for the shortest route between nodesdetermined in step 6. In case the shape vector data string informationincludes the supplementary information on link data, the route searchsection 13 uses the supplementary information to execute a route search.

[0061] Step 8: The shortest routes obtained in step 7 are sequentiallylinked to reproduce the target road section.

[0062]FIG. 1(5) shows a state where the shortest route between the nodesp₁′ and p₂′ is searched for, and the shortest route between the nodesp₂′ and p₃′ is searched for, then these routes are linked to determinethe target road section from the node p₁′ to the node p₃′. In case thePrefectural Road 123 (dotted line) bypassing the National Highway 256(thick solid line) exists as shown in FIG. 7 thus easily causing anerror in a search for the shortest routes, it is possible to reproducethe correct target road section by referencing supplementary informationsuch as the road type and road number.

[0063] When the target road section is reproduced, the event position iscalculated from the reference point of the target road section based onthe received traffic information. The event position on the map is thendisplayed by the digital map display section 15.

[0064] When nodes are intermittently selected from the target roadsection, nodes must be selected so that the positions of the nodes willnot cause an error in identifying the node positions or calculation ofroutes at the receiving side. For example, in FIG. 7, a point where theroad type changes from the national highway to the main local road isselected as the node p₂. This makes it possible to separatelyincorporate supplementary information between the nodes p₁and p₂ (roadtype, road number=national highway, 256) and supplementary informationbetween the nodes p₂ and p₃ (road type, road number=main local road,923) into the shape vector data string information, thus facilitatingreproduction of the target road section at the receiving side.

[0065] In this way, only transmission of the information on the nodesintermittently selected from the target road section is required as roadshape data to identify the target road section in this positioninformation transmission method. This considerably reduces the transmitdata amount compared with the case where coordinate line information oneach node in the target road section is transmitted.

[0066] By including supplementary information to facilitate nodeidentification and supplementary information to facilitate routeidentification into the road shape data, the receiving side can performmap matching to accurately determine the node positions and accuratelycalculate the shortest routes between the nodes, thereby faithfullyreproducing the transmitted target road section on the digital map ofits own.

[0067] This position information transmission method is especiallyadvantageous in transmitting a road shape such as mountain roads withlow road density, less intersections and winding in a complicated way.

[0068] While an example of position information transmission/receivingapparatus constituting a traffic information provision system is shownas apparatus for implementing the position information transmissionmethod, the receiving arrangement of this apparatus may be implementedin car navigation apparatus so as to provide the car navigationapparatus with the position information receiving feature by thismethod.

[0069] (Second Embodiment)

[0070] The second embodiment explains a method for including assupplementary information the intercept azimuth information in the nodeposition in the shape vector data string information in order to enhancethe matching accuracy at the receiving side in implementing a positioninformation transmission method of the first embodiment.

[0071] The intercept azimuth in the node position is the azimuth of atangent to the road curve at the node p_(x) as shown by the arrow of adotted line in FIG. 8, and displayed clockwise within the range of 0 to360 degrees, assuming the absolute azimuth of the true north as 0degrees. The intercept azimuth of the node p_(x) is obtained byaveraging the azimuth θ_(x−1) of a line connecting the node p_(x−1) andthe node p_(x−1) and the azimuth θ_(x) of a straight line connecting thenode p_(x) and the node p_(x+1) where p_(x−1) is an upstream nodeadjacent to the node p_(x) and p_(x+1) is a downstream node adjacent tothe node p_(x) as shown in FIG. 10:

(θ_(x−1)+θ_(x))/2  (Formula 1)

[0072]FIG. 11 shows the procedure for the transmitting side to obtainthe intercept azimuth of a node selected from the target road section.

[0073] Step 11: The transmitting side obtains the coordinate data of aselected node and its upstream and downstream adjacent nodes from thedigital map database.

[0074] Step 12: The transmitting side calculates the azimuths ofstraight lines connecting the nodes and uses (Formula 1) to obtain theintercept azimuth of the selected node.

[0075]FIG. 13 shows shape vector data string information including theinformation on the intercept azimuths of the nodes selected from thetarget road section as supplementary information. Here, the interceptazimuth of the start node (p₁) is displayed in absolute azimuth and theintercept azimuths of the remaining nodes in relative azimuth withrespect to the immediately preceding nodes included in the shape vectordata string information, in order to reduce the data amount.

[0076] The receiving side receives the shape vector data stringinformation and uses the information on the intercept azimuth to performmap matching. FIG. 12 shows the map matching procedure.

[0077] Step 13: The receiving side uses the data in the receiving sidedigital map database to extract positions on the road close to thelongitude/latitude data of the node p_(x) as candidates for matching inthe increasing order of the distance to the node p_(x).

[0078] Step 14: The receiving side obtains the coordinates of theadjacent node of the candidate position from the digital map database tocalculate the intercept azimuth of the candidate position. Then thereceiving side obtains the difference between the calculated interceptazimuth and the intercept azimuth of the node p_(x) sent in thesupplementary information. In case the difference is smaller than theregulated value, the receiving side determines the candidate position asa selected node.

[0079] In case the difference is larger than the regulated value, thereceiving side excludes the candidate position from candidates formatching. Execution returns to step 13 and the receiving side extractsthe next closest position as a candidate for matching and follows step14.

[0080] In this way, it is possible to prevent erroneous matching byreferencing the azimuth information on the node position.

[0081] In FIG. 8, the node p_(x) on the road 1 is likely to beerroneously matched with the road 1 passing near the point p_(x) andcrossing the road 1. In matching, as shown in FIG. 9, the receiving sidecould set the point on the road 2 closest to the point p_(x) as acandidate point 1 for matching and the point on the road 2 next closestto the point p_(x) as a candidate point 2 for matching. The candidatepoint 1 is excluded from candidates matching because the differencebetween the intercept azimuth of the candidate point 1 and that of thenode p_(x) exceeds the regulated value. The candidate point 2 isdetermined as a selected node because the difference between theintercept azimuth of the candidate point 2 and that of the node p_(x) isbelow the regulated value.

[0082] In this practice, erroneous matching of the candidate point 1 ona different road as a selected node results in an error in thecalculation of routes in the subsequent route search, thus making itimpossible to reproduce the target road section.

[0083] A position information transmission method of this embodimentincludes as supplementary information the information on the interceptazimuth at the node position into the shape vector data stringinformation. This prevents inadvertent setting of a node point on a roadcrossing the target road thus enhancing the matching accuracy.

[0084] (Third Embodiment)

[0085] The third embodiment explains a method for increasing the numberof transmit nodes at road points where the receiving side is likely tocommit erroneous matching thus enhancing the matching accuracy at thereceiving side in implementing a position information transmissionmethod of the first embodiment.

[0086] FIGS. 14(1), (2), (3), (4), and (5) are schematic views of theprocessing details in the position information transmission method onthe map.

[0087] The transmitting side, as shown in FIG. 14(1), selects a targetroad section, then the nodes to be transmitted out of the nodes in thetarget road section. In this practice, the transmitting side selects aplurality of nodes (node group) for easy identification of the differentshape of the adjacent road at sections, where the receiving side islikely to commit erroneous matching due to presence of an adjacent road,which is parallel to the target road.

[0088] The transmitting side transmits shape vector data stringinformation comprising the coordinate data of selected nodes andsupplementary information together with traffic information.

[0089]FIG. 15 illustrates the shape vector data string information. Inthis example, a transmit node includes n node groups, the node group 1has m nodes, . . . , the node group n has s nodes. While the coordinatedata of nodes included in each node group is arranged in order in thisshape vector data string information, the road shape represented by aplurality of nodes in individual node groups may be represented byFourier coefficients, approximated by arcs and straight lines, orrepresented by spline function to compress the data amount.

[0090] Meanwhile, the receiving side that has received plots the nodepositions of the nodes in each node group included in the shape vectordata string information on the map of the receiving side as shown inFIG. 14(3), then performs a map matching in order to calculate theposition of each node on the map of the receiving side as shown in FIG.14(4).

[0091] In this practice, by providing matching between the shaperepresented by the arrangement of a plurality of nodes in a node groupand the road shape on the map of the receiving side, it is possible toaccurately obtain the position of each node on the map of the receivingside.

[0092] When the node position is determined, the receiving sidesequentially searches for the shortest routes connecting the nodesintermittently located, then links the shortest routes to reproduce thetarget road section, as shown in FIG. 14(5).

[0093] In this position information transmission method, thetransmitting side selects nodes to be included in a node group based onthe following criteria:

[0094] (1) As shown in FIG. 16, when the distance L_(j) from the nodep_(j) to the closest position p _(j)′ is short and the difference(Δθ_(j)=θ_(j)−θ_(j)′) between the intercept azimuth angle θ_(j) at thenode p_(j) and the intercept azimuth angle θ_(j)′ at the node p_(j)′ issmall, the node p_(j) is determined as a node likely to be erroneouslymatched at the receiving side.

[0095] For example, the decision value ε_(j) is defined as

ε_(j) =α×L ₃β×|Δθ₃|  (Formula 2)

[0096] (where α and β are predetermined coefficients.) and when ε₃ issmaller than the regulated value ε₀, the node p_(j) is determined as anode likely to be erroneously matched at the receiving side.

[0097] (2) When the node p_(j) is a node likely to be erroneouslymatched, it is determined whether the nodes before and after the nodep_(j) are nodes likely to be erroneously matched at the receiving sidebased on the criterion under (1) and the range of nodes to be determinedis sequentially expanded until a node unlikely to be erroneously matchedat the receiving side is found. When a node unlikely to be erroneouslymatched at the receiving side, that is, a node satisfying ε_(j)≧ε₀ isfound, it is assumed that a shape that identifies itself from theadjacent road shape is obtained and the node as well as the nodessatisfying ε_(j)<ε₀ are employed as members of a node group.

[0098]FIG. 17 shows an example of a procedure for selecting nodes to beincluded in a node group.

[0099] Step 21: The target road section is selected.

[0100] Step 22: The node p_(j) to be transmitted is selected.

[0101] Step 23: Assume m=0.

[0102] Step 24: The distance L_(j±m) to the adjacent road and thedifference of intercept azimuth angle Δθ_(j±m) are calculated.

[0103] Step 25: The decision value ε_(j±m) is calculated by using(Formula 2).

[0104] Step 26: When both ε_(j−m) and ε_(j+m) are smaller than theregulated value ε₀,

[0105] Step 28: Procedure from step 24 is repeated as assuming m=m+1.

[0106] When either ε_(j−m) or ε_(j+m) is larger than the regulated valueε₀.

[0107] Step 27: P_(j−m), . . . , P_(j), . . . , P_(j+m) are employed asmembers of a node group around P_(j).

[0108] In this way, this procedure evaluates the potential for erroneousmatching of nodes at the receiving side based on the distance from anode to an adjacent road and the difference between the interceptazimuth at the node and the intercept azimuth at the closest point onthe adjacent road, and selects the nodes to be included in a node groupdepending on the evaluation value.

[0109] The transmitting side evaluates the potential for erroneousmatching of nodes at the receiving side. The transmitting side transmitsmore nodes at road points where the receiving side is likely to commiterroneous matching thus enhancing the matching accuracy at the receivingside and faithfully reproducing the target road section.

[0110] The approach for evaluating the potential for erroneous matchingof nodes at the receiving side based on the distance from a node to anadjacent road and the difference of the intercept azimuth can be appliedto a method for transmitting “road shape data” comprising shape vectordata strings as mentioned under “Background of the Invention.” It ispossible to determine the length of the road shape specified by shapevector data strings and the number of nodes to be included into theshape vector data strings depending on the evaluation value.

[0111] (Fourth Embodiment)

[0112] The fourth embodiment explains a method for supporting a casewhere the digital map data maintained by the receiving side is of anearlier version.

[0113] In a position information transmission method according to thefirst through third embodiments, the receiving side obtains the shortestroutes between nodes by way of a route search in order to reproduce thetarget road section. Thus the roads not included in the digital mapdatabase at the receiving side cannot be reproduced. For example, incase the digital map data at the receiving side is of an earlier versionand does not include the data of a road recently opened for traffic, itis impossible to connect intermittent nodes specified by thetransmitting side by using this road. As a result, the target roadsection intended by the transmitting side is different from thatreproduced by the receiving side. This will cause the receiving side toassume by mistake that an event is present on another road.

[0114] In fact, such a trouble occurs frequently in case thetransmitting side is information provision means of a trafficinformation provision system and the receiving side is car navigationapparatus provided with traffic information.

[0115] The fourth embodiment explains a position informationtransmission method for avoiding such a situation.

[0116] In this method, the transmitting side identifies the date whenthe digital map data of the target road was set, and selects the type ofthe position information transmission method used depending on thesetting date. Setting date to a digital map database for the roadsubstantially overlaps the opening period of the road. For example, whenthe target road has just been opened for traffic, the car navigationapparatus having the digital map database including the data of the newroad is very small in number. In this case, the transmitting sideemploys a position information transmission method that will avoidmisunderstanding that an event is present on a road other than thetarget road, not to mention identify the target road, even when the carnavigation apparatus has a digital map database not including the dataof the new road, in order to deliver traffic information.

[0117] In case the data setting date for the road is defined in eachroad link in the digital map database, the transmitting side employs thedate. Otherwise, the transmitting side compares the versions of thedigital map data and calculates the setting date from the revision dateof the version that first carries the road link.

[0118] The transmitting side includes the information representing thesetting date of data of the target road and the information on thedistance between nodes in the shape vector data string information.

[0119] The receiving side references the setting date of data of thetarget road in the shape vector data string information received. Whenthe receiving side has determined that the data of the target road isnot included in the digital map database of its own, it stopsreproducing the target road section.

[0120] In case the distance of the shortest route between nodes isextremely different from the distance between nodes included in theshape vector data string information, the receiving side determines thatthe data of the target road is not included in the digital map databaseof its own, and stops reproducing the target road section.

[0121] The flowchart of FIG. 18 shows the procedure at the transmittingside.

[0122] Step 30: The transmitting side selects the target road section.

[0123] Step 31: The transmitting side selects nodes to be transmitted.

[0124] Step 32: When the data setting date of the data of the roadconnecting the selected nodes is equal to or earlier than the referencedate (regulated value),

[0125] Step 33: The transmitting side employs a position informationtransmission method according to the first through third embodiments.

[0126] In case the data setting date of the data of the road connectingthe selected nodes is later than the reference date,

[0127] Step 35: The transmitting side employs a position informationtransmission method for transmitting data that directly represents theroad shape of the target road section (such as coordinate data string oneach node to identify the road shape)

[0128] Step 36: The transmitting side transmits the position informationbased on the selected method.

[0129]FIG. 20 illustrates shape vector data string information to betransmitted using a method of the invention.

[0130] This information includes the setting date of data of the roadsconnecting nodes and search distance data.

[0131] The flowchart of FIG. 19 shows the procedure at the receivingside that has received the shape vector data string information.

[0132] Step 40: The receiving side receives the information.

[0133] Step 41: The receiving side references the supplementaryinformation to determine the coordinates of each node by way of mapmatching.

[0134] Step 42: The receiving side identifies whether the data settingdate of the data between nodes included in the received data is earlierthan the creation date of map data of the local apparatus, and in caseit is earlier,

[0135] Step 43: The receiving side references the supplementaryinformation to perform a route search between nodes and determine thetarget road section.

[0136] Step 44: The receiving side identifies whether the differencebetween the distance of the determined target road section and thesearch distance between nodes included in the received data is withinthe regulated error, and in case it is within the regulated error,

[0137] Step 45: The receiving side reproduces the entire shape of thetarget road section.

[0138] In case the data setting date is not earlier than the creationdate of map data of the local apparatus in Step 42, or in case thedifference between the distance of the determined target road sectionand the search distance between nodes included in the received data isnot within the regulated error, the receiving side discards theinformation between the nodes.

[0139] By following this procedure, it is possible to avoid transmissionof erroneous position information caused by different versions of thedigital map data maintained by the transmitting side and the receivingside when a position information transmission method according to theinvention is applied.

[0140] While both the setting date of data of roads connecting nodes anddata of the search distance are included in the shape vector data stringinformation in the foregoing description, either data may be included.

[0141] While the invention has been described in detail referring toparticular embodiments, those skilled in the art will appreciate thatthe invention may be modified or corrected in various forms withoutdeparting from the spirit and the scope of the invention.

[0142] This application is based on the Japanese Patent Application No.020082/2001 filed Jan. 29, 2001, which is incorporated herein byreference.

Industrial Applicability

[0143] As understood from the foregoing description, according to amethod for transmitting position information on a digital map andapparatus for implementing the method, it is possible to efficiently andaccurately transmit the information on the shape and position on adigital map using a small amount of data, thereby enhancing the datatransmission efficiency.

What is claimed is:
 1. A position information transmission method fortransmitting and receiving road shape information and event information,and identifying an event position, the method comprising the steps of:intermittently selecting nodes in a target road section on a digitalmap; transmitting road shape information and event information;executing a map matching based on the road shape information includingcoordinate information of the selected nodes; determining positions ofthe selected nodes; obtaining a road between the selected nodes by usinga route search; identifying the target road section on the digital map;and specifying an event occurring position within the target roadsection based on the event information; wherein the road shapeinformation includes coordinate data of the selected nodes anddesignates the target road section, wherein the event informationdesignates an event occurring position by using a relative positionwithin target road section, wherein the steps of intermittentlyselecting nodes and transmitting road shape information are executed ata transmitting side, and wherein the steps of executing a map matching,determining positions, obtaining a road, identifying the target roadsection, and specifying an event occurring position are executed at areceiving side.
 2. The method according to claim 1, wherein the roadshape information transmitted from the transmitting side includessupplementary information indicating attributes of the selected nodes,and wherein the receiving side references the supplementary informationin the step of executing a map matching in order to determine thepositions of the nodes.
 3. The method according to claim 2, wherein thesupplementary information indicating the attributes of the nodesincludes at least one of a node type, a node name, a number ofconnecting links, angles between connecting links, and an interceptazimuth at the selected node.
 4. The method according to claim 2,wherein the supplementary information indicating the attributes of thenodes includes an intercept azimuth at the selected node and at leastone of a node type, a node name, a number of connecting links, andangles between connecting links.
 5. The method according to claim 1,wherein the road shape information transmitted from the transmittingside includes supplementary information indicating attributes of linksincluded between the selected nodes, and wherein the receiving devicereferences the supplementary information during using the route searchin the step of obtaining the road between the nodes.
 6. The methodaccording to claim 5, wherein the supplementary information indicatingthe attributes of the links includes at least one of a road type, a roadnumber, and a link type.
 7. The method according to claim 1, wherein thetransmitting side selects a plurality of nodes arranged around theselected node in the step of intermittently selecting nodes in thetarget road section and transmits the road shape information includingthe coordinate data of each selected node.
 8. The method according toclaim 1, further comprising the steps of: evaluating an accuracy of thematching at the receiving side based on a distance from the node to aclosest point on an adjacent road and a difference between the interceptazimuths at the node and at the closest point on the adjacent road;selecting a plurality of nodes arranged around the selected node in thestep of the intermittently selecting nodes in the target road section;and transmitting the road shape information including the coordinatedata of each selected node, wherein the steps of evaluating an accuracyof the matching, selecting a plurality of nodes, and transmitting theroad shape information are executed at the transmitting side.
 9. Themethod according to claim 1, further comprising the steps of: comparinga setting date of the digital map data of the road in the target roadsection with a regulated date; and transmitting the road shapeinformation including data representing the road shape in the targetroad section, in case of that the setting date is later than theregulated date; wherein the steps of the comparing a setting date with aregulated date and transmitting the road shape information are executedat the transmitting side.
 10. The method according to claim 1, whereinthe road shape information transmitted from the transmitting sideincludes a setting date that the digital map data of the road in thetarget road section was set, and wherein the step of identifying thetarget road section is skipped in case of that the setting date is laterthan a creation date of a digital map data which the receiving sideowns.
 11. The method according to claim 1, wherein the road shapeinformation transmitted from the transmitting side includes distancedata between the intermittently selected nodes, and the method furthercomprising the step of: comparing the distance of the road connectingthe nodes obtained by way of the route search and the distance betweenthe nodes in the road shape information; and discriminating propriety ofthe route search; wherein the steps of the comparing the distances anddiscriminating the propriety are executed at the receiving side.
 12. Themethod according to claim 1, further comprising the steps of: evaluatingan accuracy of the matching of nodes in the target road section; anddetermining a length of the target road section or number of the nodesin the road shape information based on the result of the step ofevaluating; wherein the steps of the evaluating the accuracy anddetermining the length are executed at the transmitting side.
 13. Themethod according to claim 12, wherein, in the step of evaluating theaccuracy, the accuracy of the matching is evaluated based on a distancefrom a node to a closest point on an adjacent road and the differencebetween the intercept azimuths at the node and at the closest point. 14.A position information transmission apparatus for transmitting roadshape information to specify the target road section on a digital mapand event information to specify an event position by using a relativeposition in the target road section, the apparatus comprising: positioninformation converting means for selecting a target road sectionincluding the event position; and transmit node extracting means forintermittently selecting nodes in the road shape information out of thenodes arranged on the target road section.
 15. A position informationreceiving apparatus for receiving road shape information designating atarget road section on a digital map and event information designatingan event occurring position by using a relative position in the targetroad section, the apparatus comprising: map matching means forperforming map matching to determine the positions of the nodes includedin the road shape information; and route search means for obtaining theroad connecting the nodes determined to reproduce the target roadsection.
 16. The position information receiving apparatus according toclaim 15, further comprising: map matching means for executing mapmatching based on the node information of some of the nodes included inthe road shape information to determine the positions of the nodes on adigital map.
 17. The position information receiving apparatus accordingto claim 15, further comprising: map matching means for executing mapmatching based on the node information on at least two nodes in the roadshape information in order to determine the positions of the nodes on adigital map.